EXCITATORY DRIVE FROM DEEP CEREBELLAR NEURONS TO THE SUPERIOR COLLICULUS IN THE RAT - AN ELECTROPHYSIOLOGICAL MAPPING STUDY

The cerebello-tectal projection arising from the interpositus nucleus was investigated electrophysiologically to test the hypothesis that th e deep cerebellar nuclei constitute a source of tonic excitation in th e superior colliculus. A total of 117 spontaneously active collicular neurons were recorded during GABA microinjection into 26 interpositus sites, where tonic single-cell deep cerebellar activity was also simul taneously recorded. GABA injection always led to suppression of interp ositus activity, while in the colliculus a clear pattern of results em erged. 58% of superior colliculus cells showed no response to suppress ion of interpositus activity, 35% showed a frequency decrease and 7% s howed a frequency increase. The majority of these responsive cells wer e found in a laterally located sheet of cells mainly restricted to the intermediate white layer, in close register with the known cells of o rigin of the predorsal bundle and completely overlapping the terminals of the nigrotectal pathway originating in dorsolateral substantia nig ra pars reticulata. The implications of these results for cooperative theories of head movement control involving the superior colliculus, c erebellum and precerebellar nuclei are discussed.